We have been studying the life-history of various membranous subcellular structures in identified Aplysia neurons, using intracellular pressure injection. This technique permits introduction of small volumes of concentrated radioactive substances into either the cell body or the axon. We are primarily interested in those membrane structures that are involved in the metabolism of neurotransmitter substances. These organelles (transmitter storage granules, synaptic vesicles and their precursors) are assembled in the nerve cell body and subsequently transported along the axon to nerve terminals, where they ultimately mediate synaptic transmission. Our overall objective is to study the genesis, function and fate of these organelles biochemically, morphologically, and functionally in specific identified Aplysia neurons using radiochemical radioautographic and immunological techniques. Specifically we will continue our efforts to assign the 5 major membrane glycoproteins which become rapidly labeled after intrasomatic 3H-sugar injection to specific subcellular organelles now with immunological and immunohistochemical methods to supplement the biochemical and radioautographic techniques already in use in our laboratory. Using quantitative radioautography, we plan to show that most of the membrane material moved along the axon by rapid transport consists of transmitter storage vesicles on their way to nerve endings, and that axonal vesicles in an identified serotonergic neuron undergo a developmental transformation when they reach terminal varicosities. Vesicle membrane turnover and recycling will be approached by examining specific lysosomes of identified neurons.